Rotary kiln with end and intermediate discharge

ABSTRACT

A rotary kiln is disclosed having, in material flow sequence, a drying zone, a preburning zone and a calcining zone. A provision is made for discharging a controlled portion of material from the kiln which has been dried but not calcined. Such a provision includes several radial passages projecting through the kiln shell in a common radial plane located along the kiln at approximately the end of the drying zone adjacent the preburning zone. A duct piece for each passage is connected on one end to a passage at the outer periphery of the kiln and the other end of each duct is connected to a conduit which encircles the outer periphery of the kiln shell for about one and one-quarter turns. An adjustable valve is provided in each duct to control the flow of material out of the kiln and into the encircling conduit. The encircling conduit terminates in a discharge opening which is a sufficient circumferential distance from the passages through the kiln shell, so that at least one portion of material is within the encircling conduit at all times and blocking the entry of atmospheric air into the kiln.

United States Patent [72] Inventor Whitmell ,I. Smithwick Brookiield,Wis. [21] Appl. No. 875,626 [22] Filed Nov. 12, 1969 I45] Patented Sept.14, 1971 I73 1 Assignee Allis Chalmers Manufacturing Company Milwaukee,Wis.

[54] ROTARY KILN WITH END AND INTERMEDIATE DISCHARGE 5 Claims, 2 DrawingFigs.

[52] 11.8. C1 263/33, 214/ 18 [51] Int. Cl F271) 7/32 [50] Field ofSearch 263/33, 53; 214/18 RK [56] References Cited UNITED STATES PATENTS1,707,191 3/1929 Minoque 263/33 2,002,972 5/1935 Avnsoe..... 263/332,049,734 8/1936 Fasting 263/33 2,904,322 9/1959 Bruff 214/18 RK PrimaryExaminer.lohn J. Camby Atlorneys-Arthur M. Streich, Robert B. Benson andJohn P.

Hines ABSTRACT: A rotary kiln is disclosed having, in material flowsequence, a drying zone, a prebuming zone and a calcining zone. Aprovision is made for discharging a controlled portion of material fromthe kiln which has been dried but not cal cined. Such a provisionincludes several radial passages projecting through the kiln shell in acommon radial plane located along the kiln at approximately the end ofthe drying zone adjacent the prebuming zone. A duct piece for eachpassage is connected on one end to a passage at the outer periphery ofthe kiln and the other end of each ductis connected to a conduit whichencircles the outer periphery of the kiln shell for about one andone-quarter turns. An adjustable valve is provided in each duct tocontrol the flow of material out of the kiln and into the encirclingconduit. The encircling conduit terminates in a discharge opening whichis a sufficient circumferential distance from the passages through thekiln shell, so that at least one portion of material is within theencircling conduit at all times and blocking the entry of atmosphericair into the kiln.

PATENTEO SEP 1 4197i DRYING ZONE PRE HEATING ZONE r fi ZONE r aCALCINING ROTARY KILN WITH END AND INTERMEDIATE DISCHARGE BACKGROUND OFTHE INVENTION 1. Field of the Invention This invention relates to rotarykilns and in particular to rotary kilns having a kiln shell with aprovision for discharging a portion of material passing therethrough ata location intermediate feed end and discharge end of the shell.

2. Description of the Prior Art Rotary kilns having a kiln shell with aprovision for discharging some of the material passing therethrough, atone or more locations between the ends of the kiln shell, are shown inpatents such as U.S. Pat. No. 1,731,457 of 1929, U.S. Pat. No. 2,019,397of 1935; and U.S. Pat. No. 2,039,062 of 1936. According to such priorart, hinged gate valves (as shown in FIGS. 1 and 2 of U.S. Pat. No.1,731,457) and rotating paddle wheel valves (labeled 36 in U.S. Pat. No.2,019,397 and U.S. Pat. No. 2,039,062) have been taught as devices fordischarging material, from locations intermediate the ends of a kilnshell, without admitting atmospheric air into the kiln. Thus known priorart requires actuation of a moving part each time the kiln turns todischarge material through or past such a part. It is a principal objectof the present invention, as will hereinafter be described, to eliminatedependence upon the actuation of such a moving part.

SUMMARY OF THE PRESENT INVENTION A rotary kiln according to the presentinvention, as will appear from the description to follow, not onlyachieves the aforesaid principal object relative to the described priorart, but also is particularly adapted for heating minerals for whichthere is a market need for the material in both a calcined condition anda dry but uncalcined condition. The market for such materials that havebeen dried but not calcined is sometimes a relatively small market thatdoes not easily justify the purchase, installation and operation ofdrying equipment operative solely for producing such dry but uncalcinedmaterial. It is therefore another object of the present invention toprovide a new and improved rotary kiln having provision for discharginga controlled portion of material at the end of a drying zone adjacent apreburning zone, to provide for the discharge of a marketable dry butuncalcined material as well as a fully calcined marketable material fromthe discharge end of the kiln and with improved utilization of heat inthe gases leaving the calcining and preheating zones.

In a preferred embodiment of the present invention a rotary kiln having,in material flow sequence, a drying zone, a preburning zone and acalcining zone is provided with means for discharging a controlledportion of material from the kiln which has been dried but not calcined.Such a provision includes several radial passages projecting through thekiln shell in a common radial plane located along the kiln atapproximately the end of the drying zone adjacent the preburning zone. Aduct piece for each passage is connected on one end to a passage at theouter periphery of the kiln and the other end of each duct is connectedto a conduit which encircles the outer periphery of the kiln shell forabout one and one-quarter turns. An adjustable valve is provided in eachduct to control the flow of material out of the kiln and into theencircling conduit. The encircling conduit terminates in a dischargeopening which, being spaced at least one complete turn around the kilnfrom the passages through the kiln shell, places the discharge openingof the encircling conduit a sufficient circumferential distance from thepassages through the kiln shell, so that at least one portion ofmaterial being discharged is within the encircling conduit at all timesand blocking the entry of atmospheric air into the kiln.

Other features and objects of the invention that have been attained willappear from the more detailed description to follow with reference to anembodiment of the present invention shown in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 of the accompanying drawingshows diagrammatically a side elevation of a rotary kiln feedaccordingto the present invention; and

FIG. 2 is a view taken along line ll-II in FIG. 1 and viewing thestructure in the direction indicated by'arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I, a rotarykiln 1 is shown having a cylindrical shell 2 mounted on roller supports3, 4 for rotation by drive means (not shown), to turn about a centralaxis X-X passing therethrough. The kiln 1 has material feed hood 5enclosing one end of shell 2 and hood 5 defines a gas discharge opening6. A feed chute 7 passes through the hood 5 to deposit feed materialwithin shell 2. A tiring hood 8 encloses the other end of shell 2 andprovides a primary material discharge opening 9 and a combustion airinlet 10. The firing hood also is provided with a burner assembly 11having an inlet 12 for fuel and an inlet 13 for burner air. Theoperation of the kiln I, as willbe described later, provides atemperature gradient along the axis XX of the shell 2 from firing hood 8to the feed hood 5 which provides for material moving in a counterflowrelation to gas flow, a drying zone, a preburning zone and a calciningzone, each labeled accordingly in FIG. 1.

An intermediate discharge means 16 provides a secondary materialdischarge from shell 2 at approximately the end of the drying zoneadjacent the preburning zone. Referring now to FIG. 2, the dischargemeans 16 is provided with passage means 17 comprising a plurality ofradially extending passages 18-21 projecting through shell 2 andrefractory lining 22 within shell 2, in a common radial plane Il-Il inFIG. 1. Intermediate ducts 23-26 as shown in FIG. 2 are provided whichare connected, as by welding, to the outer periphery of shell 2, toproject radially outward from passages 18-21. An encircling conduit 30is provided into which each of the ducts 23-26 open to establishmaterial flow communication from the interior of shell 2 throughpassages 18-21, through ducts 23-26, and into encircling conduit 30. Theencircling conduit 30 encircles the outer periphery of shell 2 for atleast one complete turn around shell 2 and preferably one and onequarterturns, and terminates in a discharge port 31.

Adjustable valve means, shown as a slide valve 32, is provided in eachof the ducts 23-26 for controlling the flow of material out passages182I. The valve 32 in duct 23 is shown in a fully withdrawn positionwhich opens passage 18 for full flow discharge from shell 2 into conduit30; valve 32 in duct 24 is shown in a half-withdrawn position whichprovides a partial flow therethrough and the valves 32 in ducts 25, 26are shown in a fully closed position.

In the operation of the described kiln, fuel delivered through inlet 12to the burner assembly 11 along with air through inlets l0, 13, providesthe flame and high-temperature combustion gases needed in shell 2. Thiscombustion establishes a peak temperature within shell 2 that isrelatively near, though not adjacent, the end of the shell 2 enclosed bythe firing hood 8, and a decreasing temperature gradient from thelocation of the peak temperature to the end of shell 2 enclosed by thefeed hood 5. The temperatures within shell 2 therefore define zoneswherein the kiln performs its various functions to cause reactions totake place that are required by the desired treatment of the feedmaterial. For example, to calcine Ca CO this material must be heated toabove 1,650 F. because the vapor pressure of CO in Ca CO (thedecomposition pressure) reaches atmospheric pressure at about l,650 F.Thus a calcining zone extends from the discharge end of shell 2 enclosedby firing hood 8, toward the feed end of the kiln and terminates at alocation where combustion gases are no longer hot enough to heatoncoming material to about 1,650 F. The relatively cooler gasescontinuing on toward the gas discharge opening 6, serve to preheat andthen dry the oppositely moving material. The end of the drying zoneadjacent the preheating zone, will be located where gas temperatureshave raised the temperature of feed material to about- 200300 F. Whenfeed material from chute 7 has progressed through shell 2 sufficientlyto be heated to 200-30 F., chemically uncombined water will beevaporated therefrom and the material is considered to be dry and tohave reached the end of the drying zone. From the drying zone, materialpasses into and through the preheating zone where gradual and continuousheating continues until at about 1,650" F. the material is considered tohave passed on into the calcining zone. lt is at the end of the dryingzone adjacent the preheating zone, that the intermediate discharge means16 operate to discharge controlled quantities of dry material which maybe marketed or used without calcining.

The operation of the intermediate discharge means 16, referring to FIG.2, results when rotation of shell 2 causes the radial passages 18-21 topass beneath the bed of material in the kiln. Depending upon thepositions of slide valves 32, controlled amounts of material from thebed pass through passages 18-21, ducts 23-26, and into the encirclingconduit 30. As the kiln rotates in the direction indicated by the arrowin FIG. 2, gravity causes a quantity of material in conduit 30 to moverelative to the conduit to remain beneath the shell and beneath the bedof material in shell 2. Such a quantity of material shall be controlledto be enough to fill the entire cross-sectional space of conduit 30 andblock the passage of air into the kiln. Since such a quantity ofair-blocking material within conduit 30 must travel, relative to conduit30, one and one-quarter turns around shell 2 before being discharged atport 31, a second air-blocking quantity of material will have passedinto conduit 30 before the preceding quantity has passed through port31. Thus there is at all times at least one such air-blocking quantityof material in conduit 30 and no mechanical gate or other type of airlock mechanism is needed to keep air from passing into the kiln as drymaterial is drawn off at the intermediate discharge means 16.

From the foregoing detailed description of the present invention, it hasbeen shown how the objects of the invention have been attained in apreferred manner. However, modifications and equivalents of thedisclosed concepts such as readily occur to those skilled in the art areintended to be included within the scope of this invention. Thus, thescope of this invention is intended to be limited solely by the scope ofthe claims such as are or may hereafter be appended hereto.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a rotary kiln having a cylindrical shell mounted for rotationabout a central axis therethrough, a material feed hood enclosing oneend of the shell, a firing hood with a burner and combustion air inletmeans enclosing the other end of the shell and operative to burn fueltherein and establish a temperature gradient along the axis of the shellfrom the firing hood to the feed hood which provides a calcining zone, a

preburning zone and a drying zone, and an intermediate discharge meanslocated in the kiln shell to discharge dry material from the kiln thathas passed the end of the drying zone adjacent the preheating zone, saidintermediate discharge means comprising: material discharge passagemeans through the shell of the kiln; a conduit connected to the passagemeans and encircling the outer periphery of the shell for at least onecomplete turn around the shell, to provide a discharge therethrough ofdry material from the kiln and maintain at least one conduit closingportion of such; material in the encircling conduit at all times toclose off the material discharging means from the atmosphere surroundingthe kiln; an intermediate duct between the passage means through thekiln shell and the encircling conduit; and adjustable valve meansmounted in the intermediate duct between the passage means and theencircling conduit.

2. In a rotary kiln having a cylindrical shell mounted for rotationabout a central axis therethrough, a material feed hood enclosing oneend of the shell, a firing hood with a burner and combustion air inletmeans enclosing the other end of the shell and operative to burn fueltherein and establish a temperature gradient along the axis of the shellfrom the firing hood to the feed hood which provides a calcining zone, apreburning zone and a drying zone, and an intermediate discharge meanslocated in the kiln shell to discharge dry material from the kiln thathas passed the end of the drying zone adjacent the preheating zone, saidintermediate discharge means comprising: material discharge passagemeans through the shell of the kiln; a conduit connected to the passagemeans and encircling the outer periphery of the shell for at least onecomplete turn around the shell, to provide a discharge therethrough ofdry material from the kiln and maintain at least one conduit-closingportion of such material in the encircling conduit at all times to closeoff the materialdischarging means from the atmosphere surrounding thekiln; and the material discharge passage means comprising a plurality ofradially extending passages in a common radial plane, an intermediateduct connected to'and projecting outwardly of each of the passages, andthe encircling conduit being connected to each of the intermediateducts.

3. ln a rotary kiln according to claim 2, an adjustable valve in each ofthe intermediate ducts for controlling the flow of dry material from theradially extending passages, through the intermediate ducts and into theencircling conduit for discharge therefrom.

4. in a rotary kiln according to claim 3, said encircling conduit makingat least one and one-quarter turns around the shell.

5. In a rotary kiln according to claim 3 each said adjustable valve is aslide valve arranged to move in a plain perpendicular to a central axisthrough the duct in which each such valve is provided.

1. In a rotary kiln having a cylindrical shell mounted for rotationabout a central axis therethrough, a material feed hood enclosing oneend of the shell, a firing hood with a burner and combustion air inletmeans enclosing the other end of the shell and operative to burn fueltherein and establish a temperature gradient along the axis of the shellfrom the firing hood to the feed hood which provides a calcining zone, apreburning zone and a drying zone, and an intermediate discharge meanslocated in the kiln shell to discharge dry material from the kiln thathas passed the end of the drying zone adjacent the preheating zone, saidintermediate discharge means comprising: material discharge passagemeans through the shell of the kiln; a conduit connected to the passagemeans and encircling the outer periphery of the shell for at least onecomplete turn around the shell, to provide a discharge therethrough ofdry material from the kiln and maintain at least one conduit closingportion of such material in the encircling conduit at all times to closeoff the material discharging means from the atmosphere surrounding thekiln; an intermediate duct between the passage means through the kilnshell and the encircling conduit; and adjustable valve means mounted inthe intermediate duct between the passage means and the encirclingconduit.
 2. In a rotary kiln having a cylindrical shell mounted forrotation about a central axis therethrough, a material feed hoodenclosing one end of the shell, a firing hood with a burner andcombustion air inlet means enclosing the other end of the shell andoperative to burn fuel therein and establish a temperature gradientalong the axis of the shell from the firing hood to the feed hood whichprovides a calcining zone, a preburning zone and a drying zone, and anintermediate discharge means located in the kiln shell to discharge drymaterial from the kiln that has passed the end of the drying zoneadjacent the preheating zone, said intermediate discharge meanscomprising: material discharge passage means through the shell of thekiln; a conduit connected to the passage means and encircling the outerperiphery of the shell for at least one complete turn around the shell,to provide a discharge therethrough of dry material from the kiln andmaintain at least one conduit-closing portion of such material in theencircling conduit at all times to close off the material-dischargingmeans from the atmosphere surrounding the kiln; and the materialdischarge passage means comprising a plurality of radially extendingpassages in a common radial plane, an intermediate duct connected to andprojecting outwardly of each of the passages, and the encircling conduitbeing connected to each of the intermediate ducts.
 3. In a rotary kilnaccording to claim 2, an adjustable valve in each of the intermediateducts for controlling the flow of dry material from the radiallyextending passages, through the intermediate ducts and into theencircling conduit for discharge therefrom.
 4. In a rotary kilnaccording to claim 3, said encircling conduit making at least one andone-quarter turns around the shell.
 5. In a rotary kiln according toclaim 3 each said adjustable valve is a slide valve arranged to move ina plain pErpendicular to a central axis through the duct in which eachsuch valve is provided.